1. Field of the Invention
The present invention relates generally to an information reproducing apparatus which reproduces information recorded on a recording medium and, more particularly, to an information reproducing apparatus which includes an asymmetry correction circuit.
A claim of priority is made to Japanese Patent Application No. 2005-346721, filed on Nov. 30, 2005, in the Japanese Patent Office, and Korean Patent Application No. 10-2006-0009815, filed on Feb. 1, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
2. Description of the Related Art
Hard disk drives (HDDs) are widely used as an information reproducing apparatus for devices such as, for example, computers. Furthermore, HDDs generally use magnetic recording mediums. While conventional HDDs used longitudinal magnetic recording mediums, these days perpendicular magnetic recording mediums are increasingly used in HDDs. The use of magnetic recording mediums will now be described in detail.
In a magnetic recording medium, magnetized information on the medium is detected as a voltage signal that is a vertical component of a magnetic field. This voltage signal is read out by a read head. During the detection, when asymmetry exists in a pH characteristic of the read head, a read signal becomes vertically asymmetric. This vertical asymmetry may increase the bit error rate (BER). In the conventional longitudinal magnetic recording method, the BER is generally compensated for by an asymmetry correction circuit made of a square circuit and an adder. Japanese Patent Publication No. Hei 9-320206 discloses an example of the correction of the BER.
However, the waveform of a read signal in the perpendicular magnetic recording method is different from that in the longitudinal magnetic recording method. Because of the difference between the perpendicular magnetic recording and the longitudinal recording, in the perpendicular magnetic recording method, the read signal is generally demodulated after it is closely approximated to a read signal in a longitudinal magnetic recording method by filtering it with a differential characteristic. However, despite the demodulation, the asymmetry of the read signal cannot be corrected when the filtering is performed prior to applying the signal to the asymmetry correction circuit. This is because of the use of a high pass filter (HPF) in the filtering circuit that is used for removing a low frequency component of the read signal. That is, while correction by the asymmetry correction circuit is possible in the longitudinal magnetic recording method, in the perpendicular magnetic recording method, the asymmetry cannot be corrected due to a higher cut-off frequency of a HPF.